Exhaust muffler for two-stroke cycle engine

ABSTRACT

A muffler housing with an axial inlet is shown. A tube extends axially into the housing from the inlet. A closed tuning chamber is provided in the housing surrounding the tube adjacent the inlet end. The tube has a single opening leading to the tuning chamber. A louver is mounted on the tube in the chamber to extend over the opening. The louver acts as a megaphone portion to enhance performance of the two cycle engine. The housing is provided with baffles and chambers downstream from the tuning chamber to muffle exhaust noises and further enhance performance of the engine.

0 United States Patent 1 1111 ,786,897 Swanson Jan. 22, 1974 EXHAUST MUFFLER FOR TWO-STROKE 3,462,947 8/1969 Nowak 181/53 x CYCLE ENGINE FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Ian N. Swanson, St. Paul, Minn. 1,021,641 12/1957 Germany 181/56 73 A Do ld C In 1 sslgnee gg gg fgfix c Primary ExaminerRichard B. Wilkinson Assistant ExaminerJohn F. Gonzales Filed: P 1972 Attorney, Agent, or Firm-Ralph F. Merchant et al.

[21] Appl. No.2 243,349

[57] ABSTRACT A muffler housing with an axial inlet is shown. A tube 52 1 U S Isl/54 3?) g g extends axially Into the housing from the Inlet. A [51] Int Cl 6 U08 closed tuning chamber is provided in the housing sur- [58] Fie'ld /312 314 rounding the tube adjacent the inlet end. The tube has l81/41 33 D 36 a single opening leading to the tuning chamber. A louver is mounted on the tube in the chamber to extend [56] References Cited over the opening. The louver acts as a megaphone portion to enhance performance of the two cycle en- UNITED STATES PATENTS gine. The housing is provided with baffles and cham- 3,209,858 10/1965 Jettinghoff 181/54 berg downstream from the tuning chamber to muffle exhaust noises and further enhance performance of on oeve 3,434,280 3/1969 Burkhart 60/314 the engme. 3,434,565 3/1969 Fischer 181/54 X 8 Claims, 3 Drawing Figures sli Q00 O 2600 00000 OC25 Z5 EXIIAUST MUFFLER FOR TWO-STROKE CYCLE ENGINE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the field of exhaust mufflers, and more particularly relates to an exhaust muffler for two-stroke cycle engines, which incorporates a megaphone-like device to enhance engine performance.

2. Description of the Prior Art It has long been recognized that the horsepower output of a two cycle engine is substantially affected by ex haust system design. A properly designed exhaust device or system can increase the horsepower of a two cycle engine up to 35 percent over the output of the basic engine without a muffler system. The increase in performance is greater when compared with an engine having a poorly designed exhaust system. One known method of improving two cycle engine performance is to utilize an exhaust device called a megaphone. The megaphone is an exhaust pipe having a diverging end such that a negative pressure wave is supplied to the open exhaust port at the proper time to improve scavenging. The length of the megaphone, and its crosssectional dimensions, are designed such that maximum negative pressure is supplied to the exhaust port at bottom dead center of crank shaft rotation.

Although a megaphone will improve engine performance, it will not attenuate exhaust noise. Therefore, if the noise is to be silenced, some form of muffler device must be installed downstream from the megaphone. With regard to such systems, it has also been recognized that the size of the chamber the megaphone empties into is important and that the chamber must be properly sized to achieve maximum performance. The idea of simply incorporating a megaphone, a downstream chamber, and a muffler in series has at least two basic disadvantages. For one thin, it is difficult to physically accommodate such a system within a package small enough to be used on small vehicles such as motorcycles or snowmobiles. Further, and perhaps more important, the megaphone itself generates noise which is propagated through the downstream muffler along the gas flow path. The megaphone generates noise in the sense that the noise emanating from a megaphone is greater than the noise emanating from a nondivergent tube of the same diameter as the small end of the megaphone. Therefore, in prior art systems, the megaphone placed an abnormal silencing load on the mufflers silencing element.

SUMMARY OF THE INVENTION One of the first steps leading to the present invention was my realization that if the noise being generated by the megaphone could be prevented from passing through the muffler, a good portion of the silencing load would be eliminated. The same muffler would then provide lower sound levels without creating undesirable additional resistance to gas flow. Normally, to achieve lower sound levels, it is necessary to modify the muffler such as by adding additional baffles, which increases resistance to gas flow. The increased resistance to gas flow normally reduces engine output.

The next step was my recognition that placing the tuning chamber for the megaphone outside of the gas flow path would reduce noise generation. However, I also recognized that placing the tuning chamber outside of the gas flow path while at the same time incorporating a megaphone would be highly impractical from a construction standpoint. After some further thought and experimentation, I conceived the present design. The tuning chamber is placed outside of the gas flow path and is in communication therewith by means of a single opening in the exhaust pipe, which passes through the tuning chamber. A louver is mounted over the hole in the tuning chamber to simulate a megaphone portion. The exhaust pipe extends through the tuning chamber into a downstream muffler. The results of this combination have been highly gratifying. The tuning chamber and louver act as a megaphone to enhance engine performance. However, any additional noise generated in the tuning chamber is reflected back toward the engine but is prevented by the louver from being reflected downstream toward the muffler. By reducing the noise being sent to the muffler, I was able to achieve satisfactory sound reduction with less than normal restriction to gas flow.

I have also found that adding a second closed tuning chamber at the end of the main exhaust tube substantially improves torque at low engine speeds. The chamber at the end of the main tube reflects a suitable pressure wave at low engine speeds. Because the overall system length at the end of the main tube is longer than the primary tuned length, a modified pressure wave is formed which enhances low speed torque. This improves overall performance because typically, a megaphone is less effective at low engine speeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in side elevation of an exhaust muffler according to my invention, portions thereof being broken away and portions being shown in section;

FIG. 2 is a view, primarily in section, taken along line 22 of FIG. I; and

FIG. 3 is a view in section taken along line 33 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein like reference numerals are used throughout the several views to indicate like elements of the invention, there is disclosed in FIG. I an exhaust muffler for a two-stroke cycle engine. The muffler has a generally cylindrical housing 10, the opposite ends of which are provided with end caps 11 and I2. End cap 12 is provided with an axial inlet opening defined by an outwardly extending flange 12a. Mounted along the axis of housing I0 is an exhaust inlet tube 13 having one end thereof extending from the opening in end cap 12 and the other end thereof terminating within housing 10 about threefourths of the distance from end cap 12 to end cap II. In the preferred embodiment, inlet tube 13 has a circular cross section throughout its entire length. The outer wall'of the inlet end of tube I3 is sealed to flange 12a by welding or the like to prevent gas flow therebetween.

The interior of housing I0 is divided into compartments or chambers including a closed tuning chamber 15, a resonator chamber 16, a second closed tuning chamber 17 and an exhaust gas collector compartment 18, by means of three baffle plates 19, 20 and 21. The

baffle plates l9-21 are generally circular discs each having an outer peripheral flange engaging the inner wall of housing 10 around the circumference thereof. The discs may be welded or otherwise attached to the inner wall surface of the housing 10 to prevent gas flow therebetween. Baffle plates 19 and 21) are each provided with a flanged central opening through which the exhaust inlet tube 13 extends. Again, the flanged open ings of baffle plates 19 and 20 securely engage tube 13 to prevent gas flow therebetween.

Compartment is a first tuning chamber located adjacent the inlet end of the muffler housing, between baffle plate 19 and end cap 12. In the preferred embodiment, tuning chamber 15 is a toroidal chamber surrounding inlet tube 13. A single axially and circumferentially extending opening 23 is formed in the wall of inlet tube 13 to provide communication of tube 13 with chamber 15. The single opening 23 is preferably formed approximately mid-way between the ends of tuning chamber 15 and is sized so that the area of the opening or hole 23 is approximately 70 percent of the cross-sectional area of the tube 13. In the units l have tested, this size of opening appears to give the best results. However, an opening of almost any reasonable size will give some improved results.

A metal louver 24 is mounted on the tube 13 in tuning chamber 15 to shield the opening 23. In the embodiment shown, the louver is secured by a flange 24a adjacent the upstream edge of the opening 23 around approximately three-fourths of the periphery thereof and diverges in a downstream direction over at least part of the opening, the unattached side of the louver 24 being the downstream side thereof. Preferably, the louver 24 is long enough to cover the entire opening 23, and so that the downstream edge of the louver 24 lies in a plane perpendicular to the axis of tube 13. As viewed from the downstream end of the tuning chamber 15, looking toward end cap 12, and as shown in FIG. 3, a generally oval opening is defined by the downstream end of the louver 24. As far as a two cycle engine connected to the inlet end of tube 13 is concerned, louver 24 would act like a portion of a megaphone. A portion of the sound waves emanating from the engine would enter tuning chamber 15 as indicated by the arrows in FIG. 1. The chamber 15 would resonate at a particular frequency and would reflect negative pressure waves back toward the engine to enhance scavenging. The louver 24!, however, would act as a baffle to substantially prevent reflection of sound waves through opening 23 downstream toward end cap 11. Therefore, tuning chamber 15 does not act as a noise generator to increase the noise load on the downstream muffler components.

The next downstream chamber 16 is formed between the baffle plates 19 and 20. A section of tube 13 located between baffle plates 19 and is provided with a plurality of perforations 25 to permit gas flow and sound energy to pass into chamber 16. The chamber 16 and perforations 25 act as a helmholtz resonator to provide noise cancellation within a particular frequency range.

Compartment 16 is in fluid communication with the last compartment 18 by means of a plurality of pipes 26. In the embodiment shown, there are eight of the pipes 26 equally spaced around tube 13, parallel thereto. Each pipe 26 is spaced approximately mid-way between the outer surface of tube 13 and the inner wall surface of housing 10. The pipes 26 extend through suitable openings formed in baffle plates 20 and 21, the openings being sized to prevent gas flow between the baffle plates and tubes. Therefore, the exhaust gases in compartment 16 can freely pass through pipes 26 for discharge in compartment 18. Compartment 18, which is located between baffle plate 21 and end cap ll, is provided with a radially extending outlet tube 27 from which the exhaust gases leave the housing 10.

The remaining compartment 17 is located between baffle plates 20 and 21. The downstream end of inlet tube 13 terminates at approximately the center of compartment 17. The only inlet or outlet to compartment 17 is through tube 13. Compartment 17 therefore acts as an expansion and contraction chamber to provide additional sound attenuation. In addition, this compartment or chamber 17, which surrounds the open outlet end of the exhaust tube 13 acts to enhance performance, especially at low engine speeds.

What is claimed is:

1. An exhaust muffler for two-stroke cycle engines,

comprising:

a. a generally cylindrical muffler housing having an axial opening at one end and an outlet opening at the other end;

b. an inlet tube having opposite inlet and outlet ends;

0. means mounting said inlet tube along the axis of said housing with said inlet end thereof extending from said axial opening for connection with the exhaust discharge port of an engine;

d. means forming a closed tuning chamber in said housing at least partially surrounding said tube adjacent said inlet end;

e. a wall of said tube having a single axially and circumferentially extending opening leading to said tuning chamber;

f. louver means mounted on said tube in said tuning chamber adjacent an upstream side of said opening and diverging away from said opening into said chamber in a downstream direction to shield said single opening to substantially prevent pressure waves from leaving said tuning chamber in a downstream direction while directing energy developed in the tuning chamber toward said engine to enhance the performance thereof; and

g. said housing containing silencing means downstream from said tuning chamber.

2. An exhaust muffler for two-stroke cycle engines,

comprising:

a. a generally cylindrical muffler housing having an axial opening at one end and an outlet opening at the other end;

b. an inlet tube having opposite inlet and outlet ends;

c. means mounting said inlet tube along the axis of said housing with said inlet end thereof extending from said axial opening for connection with the exhaust discharge port of an engine;

d. means forming a closed tuning chamber in said housing at least partially surrounding said tube adjacent said inlet end;

e. a wall of said tube having a single opening leading to said tuning chamber;

f. a louver mounted on said tube in said tuning chamber to shield said single opening to substantially prevent pressure waves from leaving said tuning chamber in a downstream direction while directing energy developed in the tuning chamber toward said engine to enhance the performance thereof;

g. said housing containing silencing means downstream from said tuning chamber;

h. said outlet end being open and terminating in a second closed tuning chamber in said housing; and

i. means including openings in said tube wall between the ends thereof to provide an exhaust gas flow path to said outlet opening of said housing.

3. The muffler of claim wherein said housing includes a resonator chamber at least partially surrounding said tube between said tuning chamber, said openings in said tube wall leading thereto.

4. The muffler of claim 3 including an exhaust gas collector compartment in said other end of said housing opposite said second tuning chamber from said resonator chamber, said outlet opening leading from said compartment, and a plurality of pipes leading from said resonator chamber to said compartment to permit exhaust gas flow therebetween.

5. An exhaust unit for two-stroke cycle engines, comprising:

a. a housing;

b. a tube;

0. means mounting said tube in said housing for connection with the exhaust noise and gas discharge port of an engine;

d. means forming a chamber in said housing adjacent said tube;

e. a side wall of said tube having an axially extending opening leading to said chamber to permit exhaust noise sound waves to enter said chamber; and

f. a megaphone portion mounted on the upstream edge of said opening on said tube in said chamber, said megaphone portion diverging from said opening into said chamber in a downstream direction over at least part of said opening to substantially prevent reflected sound waves from leaving said chamber in a direction away from the engine while directing sound wave energy developed in said chamber toward the engine to enhance the performance thereof.

6. The apparatus of claim 5 wherein a second chamber is formed in said housing at an outlet end of said tube to reflect sound waves so as to enhance engine performance at low engine speeds.

7. Exhaust apparatus for two-stroke cycle engines, comprising:

a. an exhaust tube having an inlet end adapted to be connected to the exhaust discharge port of an engine, an exhaust outlet end, and an axially extending opening in a side wall thereof between said ends;

b. housing means forming a tuning chamber in communication with said opening; and

c. louver means mounted on the upstream side of said opening on said tube in said chamber adjacent said opening, said louver diverging away from said opening in a downstream direction over at least part of said opening to act with said chamber as a megaphone to enhance engine performance.

8. The apparatus of claim 7 wherein the area of said opening is approximately percent of the crosssectional area of said exhaust tube. 

1. An exhaust muffler for two-stroke cycle engines, comprising: a. a generally cylindrical muffler housing having an axial opening at one end and an outlet opening at the other end; b. an inlet tube having opposite inlet and outlet ends; c. means mounting said inlet tube along the axis of said housing with said inlet end thereof extending from said axial opening for connection with the exhaust discharge port of an engine; d. means forming a closed tuning chamber in said housing at least partially surrounding said tube adjacent said inlet end; e. a wall of said tube having a single axially and circumferentially extending opening leading to said tuning chamber; f. louver means mounted on said tube in said tuning chamber adjacent an upstream side of said opening and diverging away from said opening into said chamber in a downstream direction to shield said single opening to substantially prevent pressure waves from leaving said tuning chamber in a downstream direction while directing energy developed in the tuning chamber toward said engine to enhance the performance thereof; and g. said housing containing silencing means downstream from said tuning chamber.
 2. An exhaust muffler for two-stroke cycle engines, comprising: a. a generally cylindrical muffler housing having an axial opening at one end and an outlet opening at the other end; b. an inlet tube having opposite inlet and outlet ends; c. means mounting said inlet tube along the axis of said housing with said inlet end thereof extending from said axial opening for connection with the exhaust discharge port of an engine; d. means forming a closed tuning chamber in said housing at least partially surrounding said tube adjacent said inlet end; e. a wall of said tube having a single opening leading to said tuning chamber; f. a louver mounted on said tube in said tuning chamber to shield said single opening to substantially prevent pressure waves from leaving said tuning chamber in a downstream direction while directing energy developed in the tuning chamber toward said engine to enhance the performance thereof; g. said housing containing silencing means downstream from said tuning chamber; h. said outlet end being open and terminating in a second closed tuning chamber in said housing; and i. means including openings in said tube wall between the ends thereof to provide an exhaust gas flow path to said outlet opening of said housing.
 3. The muffler of claim 10 wherein said housing includes a resonator chamber at least partially surrounding said tube between said tuning chamber, said openings in said tube wall leading thereto.
 4. The muffler of claim 3 including an exhaust gas collector compartment in said other end of said housing opposite said second tuning chamber from said resonator chamber, said outlet opening leading from said compartment, and a plurality of pipes leading from said resonator chamber to said compartment to permit exhaust gas flow therebetween.
 5. An exhaust unit for two-stroke cycle engines, comprising: a. a housing; b. a tube; c. means mounting said tube in said housing for connection with the exhaust noise and gas discharge port of an engine; d. means forming a chamber in said housing adjacent said tube; e. a side wall of said tube having an axially extending opening leading to said chamber to permit exhaust noise sound waves to enter said chamber; and f. a megaphone portion mounted on the upstream edge of said opening on said tube in said chamber, said megaphone portion diverging from said opening into said chamber in a downstream direction over at least part of said opening to substantially prevent reflected sound waves from leaving said chamber in a dIrection away from the engine while directing sound wave energy developed in said chamber toward the engine to enhance the performance thereof.
 6. The apparatus of claim 5 wherein a second chamber is formed in said housing at an outlet end of said tube to reflect sound waves so as to enhance engine performance at low engine speeds.
 7. Exhaust apparatus for two-stroke cycle engines, comprising: a. an exhaust tube having an inlet end adapted to be connected to the exhaust discharge port of an engine, an exhaust outlet end, and an axially extending opening in a side wall thereof between said ends; b. housing means forming a tuning chamber in communication with said opening; and c. louver means mounted on the upstream side of said opening on said tube in said chamber adjacent said opening, said louver diverging away from said opening in a downstream direction over at least part of said opening to act with said chamber as a megaphone to enhance engine performance.
 8. The apparatus of claim 7 wherein the area of said opening is approximately 70 percent of the cross-sectional area of said exhaust tube. 